Method for controlling an internal combustion engine

ABSTRACT

The invention concerns a method and a drive arrangement for controlling an internal combustion engine, said internal combustion engine acting via a variable transmission, particularly a continuously variable transmission, on drivable wheels or the like of a motor vehicle, in which a fuel feed to the internal combustion engine is at least reduced in dependence on an operating state and the internal combustion engine operates in overrun mode and a gear ratio of the transmission is adjusted, independently of driver intention, in dependence on at last one operating parameter of the motor vehicle.  
     It is provided that during overrun operation of the internal combustion engine ( 12 ), the gear ratio is controlled in such a way as to maximize the time interval for which the internal combustion engine ( 12 ) operates in the overrun operating state.

[0001] The invention concerns a method for controlling an internalcombustion engine, said internal combustion engine acting via a variabletransmission, particularly a continuously variable transmission, ondrivable wheels or the like of a motor vehicle, together with a drivearrangement, particularly for a motor vehicle, comprising an internalcombustion engine operatively connected via a variable transmission,particularly a continuously variable transmission, to drivable wheels orthe like.

PRIOR ART

[0002] Known from EP 0 451 887 B1, for example, is an electronicallycontrolled continuously variable transmission whose gear ratio can bevaried by means of an open-loop electronic controller. The gear ratio isadjusted in dependence on driver intention, which can be detected, forexample, from the instantaneous position of the accelerator pedal. Thegear ratio of the transmission can be adjusted with a view towarddriving performance and/or fuel economy.

[0003] It is further known to control internal combustion engines viaelectronic controllers; torque-influencing variables of the internalcombustion engine can be controlled in this case. This approach includesthe control of a fuel injection system. It is known to at least reduceor, where appropriate, completely suspend fuel injection in order toreduce pollutant emissions and fuel consumption. The internal combustionengine then operates in what is known as overrun mode.

ADVANTAGES OF THE INVENTION

[0004] The method of the invention for controlling an internalcombustion engine having the features recited in claim 1 and the drivearrangement having the features recited in claim 8 offer the advantagethat additional fuel economization and additional reduction of pollutantemissions can be achieved through engine control. Controlling the gearratio during overrun operation of the internal combustion engine in sucha way as to maximize the time interval for which the engine operates inthe overrun operating state advantageously makes it feasible to affectthe duration of overrun operation of the internal combustion engine viathe transmission control system. In particular, if the starting rotationspeed (the crankshaft rotation speed) of the internal combustion engine,that is, the crankshaft of the internal combustion engine, is adjustedvia the gear ratio in such a way that the engine control systemrecognizes that the engine is in the overrun operating state, the enginecontrol system can postpone the resumption of fuel injection to a latertime if this accords with instantaneous driver intention. This prolongsthe engine's overrun cutoff phase, resulting in reduced fuel demand andthus reduced pollutant emissions because of this prolongation.

[0005] In a preferred embodiment of the invention, it is provided thatthe gear ratio is controlled in such a way that the crankshaft rotationspeed of the engine is above a presettable threshold value thatpreferably corresponds to the current resumption rotation speed for fuelinjection to the engine. Thus, advantageously, the input rotation speed(primary rotation speed) of the transmission and consequently thecrankshaft rotation speed of the engine can be regulated to a given,selectable rotation speed value by simple control of the continuouslyvariable transmission. In this way, depending on the instantaneoustorque demand on the engine, which corresponds to driver intention, thecrankshaft rotation speed of the engine can be kept above the resumptionrotation speed for a maximum possible time interval via control of thetransmission. This extends the operation of the engine in the overrunoperating state to the maximum possible time interval, thus making itpossible to maximize the fuel savings and the reduction of pollutantemissions that are associated with overrun operation of the engine.

[0006] In addition, the drive arrangement of the invention having thefeatures cited in claim 6 offers the advantage of enabling theprolongation of the overrun cutoff phase of the engine to be implementedin motor vehicles in a simple manner. Providing means for controlling agear ratio of the transmission in such a way that an overrun operatingstate of the engine can be made to last for a maximum possible timeinterval advantageously makes it feasible to affect the overrun cutoffphase of the engine through simple transmission control means. In apreferred embodiment of the invention, these control means can beintegrated into an electronic transmission controller.

[0007] Further preferred embodiments of the invention will becomeapparent from the other features recited in the dependent claims.

DRAWINGS

[0008] The invention will now be described in more detail in the form ofan exemplary embodiment with reference to the appended drawings,wherein:

[0009]FIG. 1 is a schematic diagram of a drive arrangement of a motorvehicle;

[0010]FIG. 2 is a block diagram of the method of the invention, and

[0011]FIGS. 3 and 4 show characteristic curves of the overrun cutofffunction of the internal combustion engine according to the prior artand according to the method of the invention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0012]FIG. 1 schematically illustrates a drive arrangement 10 for amotor vehicle. Drive arrangement 10 comprises an internal combustionengine 12 whose crankshaft 14 is connected to a continuously variabletransmission 16. Crankshaft 14 is therefore the input shaft oftransmission 16. An output shaft 18 of transmission 16 is operativelyconnected to a drive axle 20, which in turn bears drivable wheels 22.Assigned to internal combustion engine 12 is an engine controller 24,and assigned to transmission 16 is a transmission controller 26. Enginecontroller 24 and transmission controller 26 can be physically separatedevices, although in a further exemplary embodiment they can also beintegrated into a common controller. Clutches, intermediate gears andthe like can be arranged between internal combustion engine 12 andtransmission 16 and between transmission 16 and drive axle 20.

[0013] The construction and manner of operation of such a drivearrangement 10 are widely known and consequently will not be examinedmore closely in this description. In general, it should be noted inaddition that torque-influencing variables of the internal combustionengine 12 are controlled by means of engine controller 24. Thesevariables include, for example, ignition control and fuel feed.Transmission controller 26 can be used to adjust the ratio of inputrotation speed, i.e. the rotation speed of crankshaft 14 in this case,to output rotation speed, i.e. output shaft 18 in this case, in aninfinitely variable and continuous manner.

[0014]FIG. 2 is a block diagram of components of the drive arrangement10 according to the invention. Engine controller 24 is connected totransmission controller 26 for purposes of data communication. Thisconnection can be made, for example, via a bus, for example a CAN[controller area network] bus. Transmission controller 26 is connectedin turn to final controlling means of the transmission 16, the gearratio of transmission 16 being able to be varied infinitely andcontinuously via appropriate drive signals. Transmission 16 is aso-called belt transmission, for example.

[0015] Engine controller 24 receives, inter alia, a signal W_(ped) thatcorresponds to the accelerator-pedal angle, i.e., the position of anaccelerator pedal. The signal therefore corresponds to instantaneousdriver intention, based on a torque demand on drive arrangement 10. Theengine controller receives, inter alia, a signal B_(ped) that indicateswhether the accelerator pedal is being actuated. If the acceleratorpedal is not being actuated, signal B_(ped)=1. Engine controller 24delivers to transmission controller 26 a signal n_(we) that correspondsto the current resumption rotation speed of crankshaft 14, below whichthe rotation speed must not fall during an overrun cutoff phase. If therotation speed falls below the resumption rotation speed n_(we), thefuel injection that was reduced or stopped during an overrun cutoffphase is resumed via engine controller 24, i.e., internal combustionengine 12 recommences combustion. Transmission controller 26 furtherreceives from engine controller 24 a signal B_(sa), which, as a logicsignal, indicates overrun cutoff “on” (B_(sa)=1) or overrun cutoff “off”(B_(sa)=0).

[0016] Transmission controller 26 receives from transmission 16 a signaln_(14actual) that corresponds to the instantaneous actual rotation speedof crankshaft 14. Transmission controller 26 delivers to transmission 16a signal n_(14nominal) that corresponds to the nominal rotation speed ofcrankshaft 14 in overrun mode, i.e., when signal B_(sa)=1. Transmissioncontroller 26 further receives another signal n_(14actual) thatcorresponds to the rotation speed of transmission output shaft 18.

[0017] Engine controller 24, transmission controller 26 and transmission16 obviously receive and output still other signals which need not beconsidered further in this description.

[0018]FIG. 3 illustrates the method of the invention in a flow chart. Ina step 28, it is first ascertained whether the conditions are met foroverrun cutoff by the internal combustion engine 12, for example byreduction or stoppage of the fuel feed. This is accomplished, forexample, by determining whether signal B_(ped) equals 1 and is smallerthan n_(sa) and whether rotation speed n_(14actual) is greater thanrotation speed n_(we). If these conditions are not present, abortion 30of the method occurs.

[0019] If the conditions are present, in a step 31 a check is performedto determine whether crankshaft rotation speed n_(14actual) has fallenbelow resumption rotation speed n_(we). If n_(14actual)<n_(we),crankshaft rotation speed n₁₄ is increased in a step 32 until crankshaftrotation speed n_(14nominal)=resumption rotation speed n_(we). Apresettable offset can be taken into account in this process, that is,rotation speed n_(14nominal) is increased to a rotation speed n_(we)+theoffset rotation speed. This increase in rotation speed in step 32 can,for example, be in an amount of 100 to 200 rpm. In this connection, apreset limit value can be specified to represent the maximum by whichthe rotation speed can be increased over the resumption rotation speedn_(we). Otherwise, the increase in rotation speed would becomenegatively apparent to the driver as a braking effect on the vehicle. Itcan also be provided that to compensate for this braking action theengine control system is also influenced, for example by the slightopening of a throttle valve in the air intake system of the internalcombustion engine 12.

[0020] If it is determined in step 31 that crankshaft rotation speedn_(14actual)≧resumption rotation speed n_(we), in step 34 a control isperformed on transmission 16 via transmission controller 26 such thatrotation speed n_(14actual) remains above resumption rotation speedn_(we), i.e., is not allowed to fall below resumption rotation speedn_(we).

[0021] It will be appreciated that both in the variant of step 32 and inthe variant of step 34, the crankshaft rotation speed n₁₄ is kept aboveresumption rotation speed n_(we) by controlling transmission 16 viatransmission controller 26. This delays the instant of resumption offuel injection to internal combustion engine 12, thus prolonging theoverrun cutoff phase of internal combustion engine 12. In a vehicle withan automatic transmission, for example, this prolongation can range from14 s to 38 s, assuming defined, identical external conditions. Clearly,a considerable prolongation of the overrun cutoff phase can be achievedunder these circumstances. The accompanying fuel economization for theinternal combustion engine can therefore amount to roughly 1% of overallfuel consumption.

[0022]FIG. 4 shows a characteristic curve of crankshaft rotation speedn_(14nominal) over time t. The resumption rotation speed n_(we) is hereassumed to be 1500 rpm. As is apparent, at instant t₁ ¹theaccelerator-pedal signal B_(ped) jumps from its logic value 0 to itslogic value 1. This occurs when accelerator-pedal angle signal W_(ped)=0or falls below a minimum threshold. That means that no torque demand isbeing placed on the internal combustion engine 12 by the driver of thevehicle at that time.

[0023] If accelerator-pedal signal B_(ped) assumes the logic value 1,this is followed at a subsequent instant t₂ by enabling of the overrunoperating state for internal combustion engine 12, i.e., signal B_(sa)assumes the logic value 1. Time interval t₁ to t₂ is used to establishwith certainty that there is in fact no torque demand on the internalcombustion engine 12 for the duration of a presettable time interval. Inaddition, the rotation speed must be below a presettable thresholdn_(sa). Crankshaft rotation speed n₁₄ decreases over time due to thelack of torque demand on the internal combustion engine 12 and is pulledout of its decline by the method of the invention above resumptionrotation speed n_(we), i.e. 1500 rpm in this case. This means that atinstant t₂ transmission controller 26 is activated to controltransmission 16, so that crankshaft rotation speed n₁₄ assumes thenominal rotation speed n_(14nominal). There follows a brief rise incrankshaft rotation speed n₁₄, with internal combustion engine 12 inoverrun mode, until this crankshaft rotation speed n₁₄ is maintainedabove resumption rotation speed n_(we). Also specified is an upperthreshold n_(s) that is equal to the resumption rotation speed n_(we)+ahysteresis (the difference between resumption rotation speed n_(we) andupper threshold n_(s)). The hysteresis establishes the maximum rotationspeed to which crankshaft rotation speed n₁₄ can be increased during theoverrun cutoff phase without any negative impact on the driving behaviorof the motor vehicle, and thus on the driving feel experienced by thedriver.

1. A method for controlling an internal combustion engine, said internalcombustion engine acting via a variable transmission, particularly acontinuously variable transmission, on drivable wheels or the like of amotor vehicle, a fuel feed to said internal combustion engine being atleast reduced in dependence on an operating state and said internalcombustion engine operating in overrun mode and a gear ratio of thetransmission being adjusted independently of driver intention independence on at least one operating parameter of said motor vehicle,characterized in that during the overrun operation of said internalcombustion engine (12), said gear ratio is controlled in such a way asto maximize the time interval for which said internal combustion engine(12) operates in the overrun operating state.
 2. The method as recitedin claim 1, characterized in that the presence of the overrun operatingstate is detected by means of at least one variable representing theoutput rotation speed (crankshaft rotation speed) of said internalcombustion engine (12).
 3. The method as recited in either of theforegoing claims, characterized in that said gear ratio is controlled insuch a way that said output rotation speed of said internal combustionengine (12) is above a presettable threshold value.
 4. The method asrecited in any of the foregoing claims, characterized in that thethreshold value of the current resumption rotation speed (n_(we))corresponds to fuel injection to said internal combustion engine (12).5. The method as recited in any of the foregoing claims, characterizedin that said output rotation speed of said internal combustion engine(12) is increased above said resumption rotation speed (n_(we)) by thetransmission control system.
 6. The method as recited in claim 5,characterized in that said output rotation speed is increased to no morethan said resumption rotation speed plus a presettable offset.
 7. Themethod as recited in any of the foregoing claims, characterized in thatthe engine control system is influenced in order to compensate for abraking effect on said motor vehicle caused by the hastening of saidoutput rotation speed.
 8. A drive arrangement, particularly for a motorvehicle, comprising an internal combustion engine that is operativelyconnected via a variable transmission, particularly a continuouslyvariable transmission, to drivable wheels (22) or the like,characterized by means via which a gear ratio of said transmission (16)is controlled in such a way that an overrun operating state of saidinternal combustion engine (12) can be made to last for a maximal timeinterval.
 9. The drive arrangement as recited in claim 8, characterizedin that said means are integrated into a transmission controller (26).